Semiconductor device and a method for fabricating the same

ABSTRACT

A semiconductor device includes a first field effect transistor (FET) including a first gate dielectric layer and a first gate electrode. The first gate electrode includes a first lower metal layer and a first upper metal layer. The first lower metal layer includes a first underlying metal layer in contact with the first gate dielectric layer and a first bulk metal layer. A bottom of the first upper metal layer is in contact with an upper surface of the first underlying metal layer and an upper surface of the first bulk metal layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 15/063,346, filed on Mar. 7, 2016, now U.S. Pat. No.10,134,872, which claims the benefit of priority to U.S. ProvisionalPatent Application 62/272,031 filed Dec. 28, 2015, the entiredisclosures of each of which are incorporated herein by reference.

TECHNICAL FIELD

The disclosure relates to a method for manufacturing a semiconductordevice, and more particularly to a structure and a manufacturing methodfor a metal gate structure.

BACKGROUND

As the semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower costs, challenges from both fabrication and design issues haveresulted in the development of three-dimensional designs, such as a finfield effect transistor (Fin FET) and the use of a metal gate structurewith a high-k (dielectric constant) material. The metal gate structureis often manufactured by using gate replacement technologies.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1A shows a top view (plan view) and FIG. 1B shows a cross sectionalview of one of the various stages of a sequential manufacturing processfor a semiconductor device according to an embodiment of the presentdisclosure.

FIG. 2 shows a cross sectional view of one of the various stages of asequential manufacturing process for a semiconductor device according toan embodiment of the present disclosure.

FIG. 3 shows a cross sectional view of one of the various stages of asequential manufacturing process for a semiconductor device according toan embodiment of the present disclosure.

FIG. 4 shows a cross sectional view of one of the various stages of asequential manufacturing process for a semiconductor device according toan embodiment of the present disclosure.

FIG. 5 shows a cross sectional view of one of the various stages of asequential manufacturing process for a semiconductor device according toan embodiment of the present disclosure.

FIG. 6 shows a cross sectional view of one of the various stages of asequential manufacturing process for a semiconductor device according toan embodiment of the present disclosure.

FIG. 7 shows a cross sectional view of one of the various stages of asequential manufacturing process for a semiconductor device according toan embodiment of the present disclosure.

FIG. 8 shows a cross sectional view of one of the various stages of asequential manufacturing process for a semiconductor device according toan embodiment of the present disclosure.

FIG. 9 shows a cross sectional view of one of the various stages of asequential manufacturing process for a semiconductor device according toan embodiment of the present disclosure.

FIG. 10 shows a cross sectional view of one of the various stages of asequential manufacturing process for a semiconductor device according toan embodiment of the present disclosure.

FIG. 11 shows a cross sectional view of one of the various stages of asequential manufacturing process for a semiconductor device according toan embodiment of the present disclosure.

FIG. 12 shows a cross sectional view of one of the various stages of asequential manufacturing process for a semiconductor device according toan embodiment of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific embodiments or examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, dimensions of elements are not limited to thedisclosed range or values, but may depend upon process conditions and/ordesired properties of the device. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact. Variousfeatures may be arbitrarily drawn in different scales for simplicity andclarity.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“made of” may mean either “comprising” or “consisting of.”

FIGS. 1A-12 show exemplary sequential manufacturing process of asemiconductor device according to one embodiment of the presentdisclosure. FIGS. 1B-12 are cross sectional views corresponding to lineX1-X1 of FIG. 1A. It is understood that additional operations can beprovided before, during, and after processes shown by FIGS. 1A-12, andsome of the operations described below can be replaced or eliminated foradditional embodiments of the method. The order of theoperations/processes may be interchangeable.

FIG. 1A shows a top view (plan view) of a structure of a semiconductordevice after dummy gate structures are formed over a substrate. In FIGS.1A and 1B, dummy gate structures 40, 41 and 42 are formed over a channellayer, for example, a part of a fin structure 20. Each of the dummy gatestructures 40, 41 and 42 corresponds to an n-channel FET, a p-channelFET and an n-type long channel FET.

The fin structure 20 is formed over a substrate 10 and extends from anisolation insulating layer 30. For explanation purpose, the dummy gatestructures 40, 41 and 42 are formed over the same fin structure 20, butin some embodiments, dummy gate structures 40, 41 and 42 are formed overdifferent fin structures, respectively. Similarly, although two finstructures 20 are illustrated in FIG. 1A, the number of fin structureper one gate structure is not limited to two, and may be one, or threeor more.

The substrate 10 is, for example, a p-type silicon substrate with animpurity concentration in a range from about 1×10¹⁵ cm⁻³ to about 1×10¹⁸cm⁻³. In other embodiments, the substrate is an n-type silicon substratewith an impurity concentration in a range from about 1×10¹⁵ cm⁻³ toabout 1×10¹⁸ cm⁻³. Alternatively, the substrate may comprise anotherelementary semiconductor, such as germanium; a compound semiconductorincluding Group IV-IV compound semiconductors such as SiC and SiGe,Group III-V compound semiconductors such as GaAs, GaP, GaN, InP, InAs,InSb, GaAsP, AlGaN, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; orcombinations thereof. In one embodiment, the substrate is a siliconlayer of an SOI (silicon-on insulator) substrate.

The fin structures 20 may be formed by trench-etching the substrate.After forming the fin structures 20, the isolation insulating layer 30is formed over the fin structures 20. The isolation insulating layer 30includes one or more layers of insulating materials such as siliconoxide, silicon oxynitride or silicon nitride, formed by LPCVD (lowpressure chemical vapor deposition), plasma-CVD or flowable CVD. Theisolation insulating layer may be formed by one or more layers ofspin-on-glass (SOG), SiO, SiON, SiOCN and/or fluorine-doped silicateglass (FSG).

After forming the isolation insulating layer 30 over the fin structures20, a planarization operation is performed, thereby removing part of theisolation insulating layer 30. The planarization operation may include achemical mechanical polishing (CMP) and/or an etch-back process. Then,the isolation insulating layer 30 is further removed (recessed) so thatthe upper regions of the fin structures 20 are exposed.

Then, the dummy gate structures 40, 41 and 42 are formed over theexposed fin structures 20. The dummy gate structure includes a dummygate electrode layer 44 made of poly silicon and a dummy gate dielectriclayer 43. Sidewall spacers 48 including one or more layers of insulatingmaterials are also formed on sidewalls of the dummy gate electrodelayer. The sidewall spacers 48 include one or more layers of insulatingmaterial such as silicon nitride based material including SiN, SiON,SiCN and SiOCN. The film thickness of the sidewall spacers 48 at thebottom of the sidewall spacers is in a range from about 3 nm to about 15nm in some embodiments, and is in a range from about 4 nm to about 8 nmin other embodiments.

The dummy gate structures further include a mask insulating layer 46,which is used to pattern a poly silicon layer into the dummy gateelectrode layers. The thickness of the mask insulating layer 46 is in arange from about 10 nm to about 30 nm in some embodiment, and is in arange from about 15 nm to about 20 nm in other embodiments.

As shown in FIG. 2, after the dummy gate structures are formed,source/drain regions 60 are formed. In the present disclosure, a sourceand a drain are interchangeably used, and the term source/drain refersto either one of a source and a drain. In some embodiments, the finstructure 20 not covered by the dummy gate structures is recessed belowthe upper surface of the isolation insulating layer 30. Then, thesource/drain regions 60 are formed over the recessed fin structure byusing an epitaxial growth method. The source/drain regions 60 mayinclude a strain material to apply stress to the channel region.

Then, as shown in FIG. 3, a first etching stop layer (ESL) 70 and afirst interlayer insulating (ILD) layer 75 are formed over the dummygate structures and the source/drain regions. The first ESL 70 includesone or more layers of insulating material such as silicon nitride basedmaterial including SiN, SiCN and SiOCN. The thickness of the first ESL70 is in a range from about 3 nm to about 10 nm in some embodiments. Thefirst ILD layer 75 includes one or more layers of insulating materialsuch as silicon oxide based material such as silicon dioxide (SiO₂) andSiON.

After a planarization operation on the first ILD layer 75 and the ESL70, the dummy gate structures are removed, thereby making gate spaces81, 82 and 83, as shown in FIG. 4. As shown in FIG. 4, the gate sidewallspacers 48 remain in the gate spaces.

Then, as shown in FIG. 5, a gate dielectric layer 85 is formed. The gatedielectric layer 85 includes one or more layers of dielectric material,such as a high-k metal oxide. Examples of the metal oxides used forhigh-k dielectrics include oxides of Li, Be, Mg, Ca, Sr, Sc, Y, Zr, Hf,Al, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and/ormixtures thereof. In some embodiments, an interfacial layer (not shown)made of, for example, silicon oxide, is formed over the fin structure(channel region) before forming the gate dielectric layer 85.

Further, a first work function adjustment (WFA) layer 90 for a p-channelFET is formed in the gate space 82. A blanket layer of a suitableconductive material is formed over the gate spaces and the first ILDlayer 75, and a patterning operation including lithography and etchingis performed to form the first WFA layer 90 for a p-channel FET in thegate space 82 (and the surrounding area). The first WFA layer 90includes one or more layers of conductive material. Examples of thefirst WFA layer 90 for a p-channel FET include Ti, TiAlC, Al, TiAl, TaN,TaAlC, TiN, TiC and Co. In one embodiment, Ti is used. The thickness ofthe first WFA layer 90 is in a range from about 3 nm to about 10 nm insome embodiments. The first WFA layer 90 may be formed by chemical vapordeposition (CVD), physical vapor deposition (PVD) including sputtering,atomic layer deposition (ALD) or other suitable method. As shown in FIG.5, the first WFA layer 90 is conformally formed in the gate space 82.

Then, a second WFA layer 95 for n-channel FETs is formed in the gatespaces 81 and 83. A blanket layer of a suitable conductive material isformed over the gate spaces and the first WFA layer 90, and a patterningoperation including lithography and etching is performed to form thesecond WFA 95 for n-channel FETs in the gate spaces 81 and 83 (and thesurrounding area). The second WFA layer 95 includes one or more layer ofconductive material. Examples of the second WFA layer 95 for ann-channel FET include TiN, TaN, TaAlC, TiC, TaC, Co, Al, TiAl, HfTi,TiSi, TaSi or TiAlC. In one embodiment, TiN is used. The thickness ofthe second WFA layer 95 is in a range from about 3 nm to about 10 nm insome embodiments. The second WFA layer 95 may be formed by chemicalvapor deposition (CVD), physical vapor deposition (PVD) includingsputtering, atomic layer deposition (ALD) or other suitable methods. Asshown in FIG. 5, the second WFA layer 95 is conformally formed in thegate spaces 81 and 83. It is noted that the order of forming the firstWFA layer 90 and the second WFA layer 95 can be changed. The second WFAlayer 95 is made of a different material than the first WFA layer 90.

Then, as shown in FIG. 6, a first metal material 101 for a first metallayer 100 is formed over the structure of FIG. 5. The first metalmaterial includes one or more layers of metal material, such as Al, Cu,W, Ti, Ta, TiN, TiAl, TiAlC, TiAlN, TaN, NiSi, CoSi, other conductivematerials. In one embodiment, TiN is used. The first metal material isformed by CVD, PVD, ALD, electroplating or other suitable methods. Thefirst metal layer 100 is made of a different material than at least oneof the first WFA layer and the second WFA layer.

Then, as shown in FIG. 7, a planarization operation is performed,thereby removing the upper portion of the deposited first metal material101. After the planarization operation, the first metal layer 100 isformed in each of the gate spaces. The planarization operation mayinclude a chemical mechanical polishing (CMP) and/or an etch-backprocess.

After each of the gate spaces are filled with the first metal layer 100,the first metal layers 100 are recessed (etched-back) to form gaterecesses 87, 88 and 89, as shown in FIG. 8. The upper portions of thefirst metal layers 100 are etched by using dry etching and/or wetetching. The amount (depth) D1 of the recessed portion is in a rangefrom about 20 nm to about 50 nm in some embodiments, and the height H1of the remaining first metal layer from the surface of the fin structure20 is in a range from about 30 nm to about 60 nm in some embodiments.

During the recess etching, the first WFA layer 90 and the second WFAlayer 95 are also etched.

Then, as shown in FIG. 9, a second metal material 111 for a second metallayer 110 is formed over the structure of FIG. 8. The second metalmaterial includes one or more layers of metal material, such as Al, Cu,Co, W, Ti, Ta, TiN, TiAl, TiAlC, TiAlN, TaN, NiSi, CoSi, otherconductive materials. In one embodiment, W or Co is used. The secondmetal material is formed by CVD, PVD, ALD, electroplating or othersuitable methods. The second metal material 111 is made of a differentmaterial than the first metal material (and the first and second WFAlayers) and has a higher durability against a gas containing Cl and/or Fthan the first metal material 101 (and the first and second WFA layers).

A planarization operation is subsequently performed, thereby removingthe upper portion of the deposited second metal material 111. After theplanarization operation, the second metal layer 110 is formed in each ofthe gate spaces. The planarization operation may include a chemicalmechanical polishing (CMP) and/or an etch-back process.

The planarized second metal layers 110 are further recessed in the gatespaces by using an etch-back operation, as shown in FIG. 10. The amount(depth) D2 of the recessed portion is in a range from about 10 nm toabout 40 nm in some embodiments, and the thickness T1 of the remainingsecond metal layer 110 from the upper surface of the first metal layer100 is in a range from about 10 nm to about 30 nm in some embodiments.As shown in FIG. 10, a bottom of the second metal layer 110 is incontact with an upper surface of the first metal layer 100 and an uppersurface of the first and/or second WFA layers 90, 95.

Then, as shown in FIG. 11, cap insulating layers 120 are formed over thesecond metal layers 110. The cap insulating layer 120 includes one ormore layers of insulating material such as silicon nitride basedmaterial including SiN, SiCN and SiOCN.

To form the cap insulating layers 120, a blanket layer of an insulatingmaterial having a relatively large thickness is formed over structure ofFIG. 10, and a planarization operation, such as a CMP, is performed.

Then, a second ILD 130 is formed over the structure of FIG. 11, and apatterning operation is performed to form via holes. The via holes arefiled with one or more conductive materials, thereby forming via plugs140, 142, 144, 146 and 148, as shown in FIG. 12. As shown in FIG. 12, awidth W1 along the X direction (a second lateral direction perpendicularto the first lateral direction) of the wide gate electrode is greaterthan a width W2 along the X direction of the narrow gate electrode.Further, one or more metal wirings (not shown) are formed over the viaplugs, respectively. A dual damascene method may be used to form the viaplugs and the metal wirings.

In the above embodiment, the second metal layers are formed by using ablanket deposition, a planarization operation and an etch-backoperation. In another embodiment, the second metal layers are directlyformed over the first metal layers. For example, after the structure ofFIG. 8 is formed, a selective deposition of W or Co is used to form thesecond metal layer over the first metal layers only in the gate spaces,to obtain the structure shown in FIG. 10. For example, by using an ALDmethod, Co and W can be selectively grown on the metal layers 90, 95 and100, while Co or W are not grown on SiO₂, SiN or other dielectricmaterials.

It is understood that the device shown in FIG. 12 undergoes further CMOSprocesses to form various features such as interconnect metal layers,dielectric layers, passivation layers, etc. In the above embodiment, themanufacturing operations for a Fin FET are described. However, the abovemanufacturing process may be applied to other types of FET, such as aplanar type FET.

The various embodiments or examples described herein offer severaladvantages over the existing art. For example, in the presentdisclosure, as shown in FIG. 12, the via plugs 140, 144 and 148 are incontact with the second metal layers 110. When via holes for the viaplugs 140, 144 and 148 are formed, a dry etching using a gas containingCl and/or F is used. If the second metal layers 110, which have a higherdurability against Cl or F, are not used, the Ti or TiN layer exposed inthe bottoms of the contact holes would be damaged (e.g., causingerosion) by the Cl or F component in the etching gas. In contrast, inthe present embodiment, since the second metal layers 110, which have ahigher durability against Cl or F that Ti and TiN, are used, damage tothe Ti or TiN layers can be avoided.

It will be understood that not all advantages have been necessarilydiscussed herein, no particular advantage is required for allembodiments or examples, and other embodiments or examples may offerdifferent advantages.

According to one aspect of the present disclosure, in a method ofmanufacturing a semiconductor device, a dummy gate structure is formedover a substrate. A source/drain region is formed. A first insulatinglayer is formed over the dummy gate structure and the source/drainregion. A gate space is formed by removing the dummy gate structure. Thegate space is filled with a first metal layer. A gate recess is formedby removing an upper portion of the filled first metal layer. A secondmetal layer is formed over the first metal layer in the gate recess. Asecond insulating layer is formed over the second metal layer in thegate recess.

According to another aspect of the present disclosure, in a method ofmanufacturing a semiconductor device, a first dummy gate structure and asecond dummy gate structure are formed over a substrate. Source/drainregions are formed. A first insulating layer is formed over the firstand second dummy gate structures and the source/drain regions. A firstgate space and a second gate space are formed by removing the first andsecond dummy gate structures, respectively. A first metal layer isformed in the first gate space, and a second metal layer is formed inthe first and second gate spaces. After forming the first and secondmetal layers, the first and second gate spaces are filled with a thirdmetal layer. A gate recess is formed by removing upper portions of thefirst, second and third metal layers formed in the first gate space, anda second gate recess is formed by removing upper portions of the firstand third metal layers formed in the second gate space. A first gateelectrode and a second gate electrode are formed by forming metal layersin the first and second gate recesses. Second insulating layers areformed over the fourth metal layers in the first and second gate recess.

In accordance with yet another aspect of the present disclosure, asemiconductor device includes a first field effect transistor (FET)including a first gate dielectric layer and a first gate electrode. Thefirst gate electrode includes a first lower metal layer and a firstupper metal layer. The first lower metal layer includes a firstunderlying metal layer in contact with the first gate dielectric layerand a first bulk metal layer. A bottom of the first upper metal layer isin contact with an upper surface of the first underlying metal layer andan upper surface of the first bulk metal layer.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A semiconductor device comprising: a first fieldeffect transistor (FET) including a first gate dielectric layer and afirst gate electrode, wherein: the first gate electrode includes a firstlower metal layer and a first upper metal layer, the first lower metallayer includes a first underlying metal layer in contact with the firstgate dielectric layer and a first bulk metal layer fully filling a spaceformed by the first underlying metal layer, the first underlying metallayer is made of Ti, the first bulk metal layer is made of TiN, and abottom of the first upper metal layer is in contact with an uppersurface of the first underlying metal layer and an upper surface of thefirst bulk metal layer.
 2. The semiconductor device of claim 1, whereinthe first upper metal layer includes at least one of Co, W, Ti, Al, andCu.
 3. The semiconductor device of claim 1, wherein the first uppermetal layer is made of Co.
 4. The semiconductor device of claim 1,further comprising a cap insulating layer disposed on the first gateelectrode.
 5. The semiconductor device of claim 4, further comprisingsidewall spacers disposed on opposing side faces of the first gateelectrode and the cap insulating layer.
 6. The semiconductor device ofclaim 5, further comprising: an interlayer dielectric (ILD) layer and anetching stop layer disposed between the interlayer dielectric layer andone of the sidewall spacers.
 7. The semiconductor device of claim 6, theetching stop layer is one of SiN, SiCN and SiOCN.
 8. The semiconductordevice of claim 6, further comprising a source/drain epitaxial layer incontact with one of the sidewall spacers, wherein the etching stop layeris in contact with an upper surface of the source/drain epitaxial layer.9. The semiconductor device of claim 8, further comprising asource/drain contact passing through the ILD layer and the etching stoplayer and in contact with the source/drain epitaxial layer.
 10. Thesemiconductor device of claim 8, further comprising a gate contactpassing through the cap insulating layer and in contact with the firstupper metal layer.
 11. The semiconductor device of claim 1, furthercomprising: a second FET including a second gate dielectric layer and asecond gate electrode, wherein: the second gate electrode includes asecond lower metal layer and a second upper metal layer, the secondlower metal layers includes a second underlying metal layer in contactwith the second gate dielectric layer, a third underlying metal layerand a second bulk metal layer fully filing a space formed by the thirdunderlying metal layer, the second underlying metal layer is made ofTiN, the third underlying metal layer is made of Ti, the second bulkmetal layer is made of TiN, and a bottom of the second upper metal layeris in contact with an upper surface of the second underlying metallayer, an upper surface of the third underlying metal layer and an uppersurface of the second bulk metal layer.
 12. The semiconductor device ofclaim 1, further comprising: a second field effect transistor (FET)including a second gate dielectric layer and a second gate electrode,wherein: the second gate electrode includes a second lower metal layerand a second upper metal layer, the second lower metal layer includes asecond underlying metal layer in contact with the second gate dielectriclayer and a second bulk metal layer fully filling a space formed by thesecond underlying metal layer, the second underlying metal layer is madeof Ti, the second bulk metal layer is made of TiN, a bottom of thesecond upper metal layer is in contact with an upper surface of thesecond underlying metal layer and an upper surface of the second bulkmetal layer, and a width of the second gate electrode is greater than awidth of the first gate electrode, along a lateral directionperpendicular to a lateral direction in which the first and second gateelectrodes extend.
 13. A semiconductor device, comprising: an FETincluding a gate dielectric layer and a gate electrode, wherein: thegate electrode includes a lower metal layer and a upper metal layer, thelower metal layers includes a first underlying metal layer in contactwith the first gate dielectric layer, a second underlying metal layerand a bulk metal layer fully filing a space formed by the secondunderlying metal layer, the first underlying metal layer is made of TiN,the second underlying metal layer is made of Ti, the bulk metal layer ismade of TiN, and a bottom of the upper metal layer is in contact with anupper surface of the first underlying metal layer, an upper surface ofthe second underlying metal layer and an upper surface of the bulk metallayer.
 14. The semiconductor device of claim 13, wherein the first uppermetal layer includes at least one of Co, W, Ti, Al, and Cu.
 14. Thesemiconductor device of claim 13, wherein the first upper metal layer ismade of Co.
 15. The semiconductor device of claim 13, furthercomprising: a cap insulating layer disposed on the first gate electrode;and sidewall spacers disposed on opposing side faces of the first gateelectrode and the cap insulating layer.
 16. The semiconductor device ofclaim 15, further comprising: an interlayer dielectric (ILD) layer andan etching stop layer disposed between the interlayer dielectric layerand one of the sidewall spacers.
 17. The semiconductor device of claim16, the etching stop layer is one of SiN, SiCN and SiOCN.
 18. Thesemiconductor device of claim 16, further comprising a source/drainepitaxial layer in contact with one of the sidewall spacers, wherein theetching stop layer is in contact with an upper surface of thesource/drain epitaxial layer.
 19. A semiconductor device, comprising: afirst FET including a first gate dielectric layer and a first gateelectrode; and a second FET including a second gate dielectric layer anda second gate electrode, wherein: a gate length of the first FET issmaller than a gate length of the second FET, the first gate electrodeincludes a first lower metal layer and a first upper metal layer, thefirst lower metal layers includes a first underlying metal layer incontact with the first gate dielectric layer, a second underlying metallayer disposed on the first underlying metal layer and a first bulkmetal layer fully filing a space formed by the second underlying metallayer, the second gate electrode includes a second lower metal layer anda second upper metal layer, the second lower metal layer includes asecond underlying metal layer in contact with the second gate dielectriclayer and a second bulk metal layer fully filling a space formed by thesecond underlying metal layer, the first underlying metal layer is madeof TiN, the second underlying metal layer is made of Ti, the first bulkmetal layer is made of TiN, the second underlying metal layer is made ofTi, and the second bulk metal layer is made of TiN.
 20. Thesemiconductor device of claim 19, wherein: the first gate electrodeconsists of the first underlying metal layer, the second underlyingmetal layer, the first bulk metal layer and the first upper metal layer,and the second gate electrode consist of the second underlying metallayer, the second bulk metal layer and the second upper metal layer.